Fort Duncan was built on land owned by John Twohig that the U.S. government neither purchased nor leased from him for several years, a practice the War Department followed at other border forts. It was only after the U.S. Army signed a lease in the late 1850s that construction of permanent buildings of limestone began. The fort was occupied during the Civil War by a squadron of the Confederate Frontier Regiment and was not reoccupied by federal troops until 1868. By the 1880s, Fort Duncan had eighteen structures, including barracks, officers’ quarters, storehouses for supplies and powder, and a hospital. The War Department closed Fort Duncan in 1883, reopened it with a small contingent in 1890, made it a major training site for the Army in 1917, and closed it in 1922. Among those who served at Fort Duncan were the Black Seminole Indian Scouts, a group of multiracial scouts originally from Florida who had lived for nearly twenty years in Hacienda de Nacimiento in Coahuila. They were recruited by the U.S. Army to protect the region from Indian attacks and garrisoned here for three years before being transferred to Fort Clark (EL8).
The City of Eagle Pass purchased the fort property for a park in 1938. Crews from the Works Progress Administration (WPA), who also constructed the handsome terracing on the nearby arroyo separating the fort grounds from the city, undertook rehabilitation work on the long-abandoned fort buildings. Today, seven buildings remain, most dating from the 1850s through the 1870s. The fort headquarters building at 310 Bliss Street is now the Fort Duncan Museum. The whitewashing that covers the other buildings at the fort has been removed from the front of the museum, revealing that it was constructed in three sections: a central building of roughly shaped limestone slabs, a later limestone addition to the right, and a brick ell added in the early twentieth century.